UV cure technology is a green coating technology characterized by high productivity, low energy consumption and extremely low VOC emission. It is a promising materials fabrication technology that is enjoying fast-pace market expansion.
Natural plant oils have been used to prepare bio-based UV curable materials via various chemical approaches. Acrylated epoxidized soybean oil (known as AESO or ASO) was synthesized via the acrylation of epoxidized soybean oil (Lu et al., Polymer, 2005, 46:71-80; Pelletier et al., J. Applied Polymer Science, 2006, 99:3218-3221) and commercialized by Cytec Industries etc. (Pashley et al., 1994, U.S. Pat. No. 5,360,880). Acrylated sunflower oil has recently been prepared by a new route, which involved an “ene” reaction with singlet oxygen (de Espinosa et al., 2009, J. Polym. Sci., Part A: Polym. Chem., 47:1159-1167). Further development of these bio-based UV curable materials is based on chemical modifications aimed at increasing the Tg and enhancing their performance. For example, AESO can be reacted with maleic acid to increase the carbon-carbon double bonds content, which increases the crosslinking density of the resulting biopolymers; the reaction of AESO with cyclohexane dicarboxylic acid also formed oligomers, which increased the Tg of resulting biopolymers by introducing stiff cyclic rings into the structure (Khot et al., 2001, J. Appl. Polym. Sci., 82:703-723). A series of UV-curable oligomers based on allyl, acrylate or vinyl ether functionalized castor oil were synthesized by isocyanate prepolymer process, these biobased oligomers exhibited excellent thin film performance when blended with multifunctional thiols as thiol-ene UV curable formulation (Black and Rawlins, 2009, Eur. Polymer J. 45:1433-1441).
Other than direct modifications of plant oils, the introduction petroleum-based chemicals into plant oil derivatives is another promising approach to increase bio-based UV curable materials performance. For example, UV curable hyperbranched polyether was obtained by transesterification of hyperbranched polyol and epoxy functional methyl vernoleate from crude vegetable oil (Samuelsson et al., 2004, Progress in Organic Coatings 50:193-198). A series of UV-curable urethane acrylates (UV-PUs) based on epoxidized plant oil monoglyceride were prepared by using novel polyols derived from plant oils reacted with isocyanate. UV curable coatings that are based on these UV-PUs show good curing characteristics and potential for high-performance industrial coating applications (Patel et al., 2008, J. Applied Polymer Science 107:71-81; Mannari and Patel, “Novel “Green” UV-curable Oligomers—Leveraging Chemistry for Delivering Value,” presented at the RadTech UV and EB Technology Expo & Conference; May 24-26, 2010, Baltimore, Md.). In all these examples, however, the introduction of petroleum-based ingredients led to lower biorenewable content. Coating materials with higher biorenewable content and good performance are highly desired.